1. Field of the Invention
The present invention relates to a mold for forming a golf ball cover layer. More specifically, the present invention relates to a mold for forming a thermoset polyurethane cover for a golf ball.
2. Description of the Related Art
Golf balls may comprise one-piece constructions or they may include several layers including a core, one or more intermediate layers and an outer cover that surrounds any intermediate layer and the core. In multi-component golf balls, there exists an inner core. Often, this core is made by winding a band of elastomeric material about a spherical elastomeric or liquid-filled center. Alternatively, the core may be a unitary spherical core made of a suitable solid elastomeric material. One such material that is conventionally used for the core of golf balls is a base rubber, such as polybutadiene, which is cross-linked with a metal acrylate, such as zinc diacrylate.
In the construction of some multi-component golf balls, an intermediate boundary layer is provided outside and surrounding the core. This intermediate boundary layer is thus disposed between the core and the outer cover of the golf ball.
Located outwardly of the core and any intermediate boundary layer is a cover. The cover is typically made from any number of thermoplastic or thermosetting materials, including thermoplastic resins such as ionomeric, polyester, polyetherester or polyetheramide resins; thermoplastic or thermoset polyurethanes; natural or synthetic rubbers such as balata (natural or synthetic) or polybutadiene; or some combination of the above.
Golf balls are typically manufactured by various molding processes, whether one-component or multicomponent balls. Generally, the core of the golf ball is formed by casting, compression molding, injection molding or the like. If an intermediate boundary layer is desired, one or more intermediate boundary layers are added over the core by any number of molding operations, including casting, compression molding, and/or injection molding. The cover is then formed over the core and intermediate boundary layers, if present, through casting, compression molding, and/or injection molding.
One of the earliest disclosures of manufacturing a golf ball with dimples is set forth in U.S. Pat. No. 721,462 to Richards, which was filed on May 26, 1902. Richards discloses covering a core that is centered with pins within a spherical cavity of a mold, with a fluent gutta percha material. The gutta percha material is subjected to high pressure and then cooled within the mold to form a cover on the core.
Bowerman et al., U.S. Pat. No. 2,940,128, which was filed on May 14, 1958, discloses a method of manufacturing a rubber covered golf ball. Bowerman discloses separately forming rubber hemispherical covers on the core.
One of the earliest methods of manufacturing a polyurethane cover is disclosed in Gallagher, U.S. Pat. No. 3,034,791, which was filed on Apr. 26, 1960. Gallagher discloses forming polyurethane disks that are then molded over cores to create a polyurethane cover.
Another early method of manufacturing a polyurethane cover is disclosed in Ward, U.S. Pat. No. 3,147,324, which was filed on Oct. 20, 1960. Ward discloses using a liquid polyurethane prepolymer, either polyether-type or polyester-type, that is cured with a diamine. The liquid polyurethane is poured into a hemispherical mold cavity of a mold half, and a wound golf ball core is centered therein. Subsequently, a corresponding hemispherical mold cavity of a second mold half is filled with the liquid polyurethane. The first mold half with the wound core is then mated with the second mold half and allowed to cure for a set period of time.
A second Ward patent directed toward forming a polyurethane cover is U.S. Pat. No. 3,112,521, which was filed on Mar. 8, 1961. The '521 Ward patent discloses a method and apparatus for sensing the center of a wound core prior to placement in a mold filled with liquid polyurethane which is part of a complete casting machine. As with the '324 Ward patent, liquid polyurethane is poured into a hemispherical mold cavity of a mold half. However, in the '521 Ward patent, the wound core is more precisely centered prior to insertion into the polyurethane filled cavity. The entire process of the '521 Ward patent is performed on a rotatable annular platform.
Another example of a method for making a polyurethane cover is disclosed in Watson et al., U.S. Pat. No. 3,130,102, filed originally in Great Britain on May 19, 1960. Watson discloses a process for partially forming polyurethane half-shells for a golf ball, cooling them, then fusing them together on a core while imparting a dimple pattern thereon. Watson also demonstrates better cutting resistance for its polyurethane covered golf ball. An alternative of the Watson process for making a polyurethane cover on a golf ball is disclosed in a related patent to Ford et al., U.S. Pat. No. 3,177,280, filed originally in Great Britain on May 23, 1960. Ford discloses coating a core until the required thickness is applied, however, it still requires interrupting the curing, to place the coated core into a mold to impart a dimple pattern thereon.
Building upon Ford and Watson, U.S. Pat. No. 3,989,568 to Isaac discloses a process for using curing agents that have different reaction rates to partially cure a polyurethane half shell that is later placed on a core for further processing. Isaac discloses that a cover may be as thin as 0.025 inches using this process which involves two different diisocyanates and different amine curing agents. Dusbiber, U.S. Pat. No. 3,979,126, originally filed in February of 1965, discloses another method of making polyurethane half shells for a golf ball cover.
Brown et al., U.S. Pat. No. 5,006,297, filed on Feb. 22, 1989, discloses openly curing both halves of polyurethane cover in an initial mold, then compression molding the smooth covered golf ball to form a dimple pattern thereon. The initial molding step may use retractable or non-retractable pins to center the wound core while polyurethane flows about it.
Wu, U.S. Pat. No. 5,334,673 discloses the multiple step process of Ford and Watson using a slow-reacting polyamine curing agent. Wu et al., U.S. Pat. No. 5,692,974 discloses the difficulty in manufacturing a commercially viable polyurethane covered golf ball due to the centering of the core within a partially cured mixture of polyurethane. The '974 Wu patent states that the 1993 Titleist®PROFESSIONAL was the first successful polyurethane covered golf ball.
Calabria et al., U.S. Pat. Nos. 5,733,428; 5,888,437; 5,897,884; and 5,947,843 all originate from an application filed on Jan. 21, 1994 which was a continuation-in-part application of an abandoned application filed on Jul. 6, 1992. The Calabria family of patents disclose a method and apparatus for forming a wound core golf ball with a polyurethane cover. The apparatus of Calabria, similar to that of the '521 Ward patent, inserts a wound core into a half mold cavity of partially cured polyurethane. Calabria discloses using a single insertion device for each individual mold. Calabria introduces the polyurethane mixture into a top mold half and after 50 to 80 seconds later a core is lowered at a controlled rate to prevent air bubbles, and a stop limits the downward movement of the core into the mold cavity. At a later time the bottom mold halves are filled with the polyurethane mixture. After another 50 to 80 seconds, the vacuum holding the core is released and mold halves are removed from the centering fixture. The top mold halves are then mated with the bottom mold halves and excess material resides in sprue channels. The mold halves are heated and pressurized for a predetermined period of time, and then demolded.
Herbert et al., U.S. Pat. No. 5,885,172, which was filed on May 27, 1997, discloses using the process of Calabria to form a polyurethane cover over a core with an inner layer thereon. Wu, U.S. Pat. No. 5,908,358, which was originally filed on Jun. 7, 1995, discloses using a four mold unit to manufacture golf balls with polyurethane covers.
Dewanjee, et al., PCT International Publication Number WO 99/43394, claiming priority from U.S. patent application Ser. No. 09/030,332, filed on Feb. 25, 1998 discloses a method for forming a polyurethane cover on a golf ball. Dewanjee discloses using a X-Y table to position mold halves under a mix head that dispenses the polyurethane mixture. The mold halves are then placed on a conveyor for transport to a core insertion station. The cores are then centered over each cavity through use of a pin on the mold half that engages with an aperture on the core holding unit. A second mold half is mated with the first mold half, and the mold is heated under pressure to form a polyurethane cover over the core. De-molding is accomplished through insertion of mold releasing pins into apertures of the mold halves.
In most any casting or molding process, a flash ring—or what resembles a “Saturn ring” appears where the cavities join and the excess material spills over into a trough. This allows for escape of the excess material during the casting process, and ensures consistent thickness. What results is a cast golf ball cover with a small flash ring or seam around the circumference. The seam is then buffed away, and the ball is finished or painted, making the line nearly imperceptible. However, the continuous line does cause the dimples to be slightly farther apart at the equator, which can affect the golf ball″s aerodynamics.
Thus, there remains a need for a casting mold that will minimize the flash ring and allow for the dimples to be positioned closer across the equator of the golf ball.